After commit 3fb16866b51d ("driver core: fw_devlink: Make cycle
detection more robust"), fw_devlink prints an error when consumer
devices don't have their fwnode set. This used to be ignored silently.
Set the fwnode mipi_dsi_device so fw_devlink can find them and properly
track their dependencies.
This fixes errors like this:
[ 0.334054] nwl-dsi 30a00000.mipi-dsi: Failed to create device link with regulator-lcd-1v8
[ 0.346964] nwl-dsi 30a00000.mipi-dsi: Failed to create device link with backlight-dsi